Crosslinked foams have a low specific gravity, namely are lightweight, and have flexibility and high mechanical strength. They have been widely used for interior and exterior materials of construction, automobile components such as interior materials and door glass run channels, packaging materials, and daily necessities. Merely foaming a resin provides lightweight but results in a foam having low mechanical strength. It is thus publicly known that molecular chains in the foam are linked to each other by crosslinking reaction of the resin to prevent mechanical strength from being decreased.
Crosslinked foams made of resin find use in footwear and footwear components such as shoe soles (mainly mid soles) of sport shoes and the like. The reason for this use is that footwear and footwear components are required to meet conditions such as lightness in weight, resistance to deformation by long use, and mechanical strength and impact resilience to withstand use under severe conditions.
It is widely known that crosslinked foams made of ethylene/vinyl acetate copolymers have been used for shoe soles. However, crosslinked foams molded from compositions of ethylene/vinyl acetate copolymers have a high specific gravity and a large compression set. In the case in which the crosslinked foam is used for a shoe sole, the shoe sole is heavy and is compressed after long use, and mechanical strength such as impact resilience is decreased disadvantageously.
Patent documents 1 and 2 describe a crosslinked foam using an ethylene/α-olefin copolymer and a crosslinked foam using a mixture of an ethylene/vinyl acetate copolymer and an ethylene/α-olefin copolymer, respectively. These inventions improve low specific gravity and compression set. However, a satisfactory performance cannot be obtained.
Patent document 3 describes an ethylene/α-olefin/specified non-conjugated polyene random copolymer. However, a study by the present inventors has found that there is room for improvement in terms of providing a foam having a low specific-gravity, a small compression set (CS) and a uniform quality.
Patent document 4 describes an olefin crosslinked foam and a composition therefor. However, a study by the present inventors has found that there is room for improvement in terms of providing a foam having a lower specific gravity and a smaller compression set.
Patent document 5 describes an elastomer composition for a crosslinked foam and applications thereof. However, a study by the present inventors has found that there is room for improvement in terms of providing a foam having a low specific gravity and a small compression set (CS).
Patent document 1: Japanese Unexamined Patent Application Publication No. 9-501447
Patent document 2: Japanese Patent Application Laid-Open Publication No. 11-206406
Patent document 3: Japanese Patent Application Laid-Open Publication No. 11-5818
Patent document 4: EP 997493
Patent document 5: EP 1229076